1. Technical Field of the Invention
This invention generally relates to fiber optic connector polishing fixtures.
2. Description of Related Art
Fiber optic cables are increasingly being used for communicating wide bandwidths of data at high data transmission rates. The use of fiber optics typically becomes cost efficient as compared, for instance, to copper cables, when the data rates exceed about 100,000 bits per second (bps). The applications for fiber optic cables vary widely, from telecommunications, to cable television, to highly advanced aircraft and spacecraft systems. With the increased trend to automate the manufacturing of fiber optic cables and with diminishing material costs, the use of fiber optics is apt to become more widespread in arenas with less demanding telecommunications requirements, such as, for example, in many automotive applications. The use of fiber optic cables is advantageous in many respects. Fiber optic cables have a low weight, a low material cost, and are of a much smaller size as compared with conventional twisted-shielded pairs of copper wires.
Despite the above advantages of fiber optic cables, and many more not mentioned above, the manufacturing of the cables to required standards, and in particular with respect to fiber optic termini, presents problems for a number of reasons. One of these problems is related to the precision with which the terminus of a fiber optic cable is polished. The xe2x80x9cterminusxe2x80x9d in the context of the instant description refers to a combination of a rigid ferrule and of a fiber optic filament concentrically supported therein. It is well known that one of the preparation steps of a fiber optic cable involves the polishing of its terminus. Most fiber optic assemblies are fabricated by bonding a connector, including its ferrule, to an optical fiber. After this bonding step, excess fiber optic filament protruding from the exposed end of the connector ferrule is cleaved in preparation for polishing.
Generally, a coarse hand polish is performed on the terminus, such as, for instance, by holding the terminus in a puck and by moving it over a polishing surface. The coarse polish is then followed by a fine polish performed also by hand or with a machine. Conventionally, the ferrule of the terminus is polished such that it presents a convex end face, the apex of which must ideally be intersected by the centerline of the fiber optic filament. Any offset of the apex of the polished end face of the ferrule with respect to the centerline of the fiber optic filament, hereinafter referred to as xe2x80x9capex offset,xe2x80x9d affects the efficiency of spectral transmission between pairs of fiber optic cable termini placed face to face with respect to one another for transmitting data therebetween. In advanced fiber optic system designs, precision polishing is required due to stricter connector polishing requirements now being imposed. Polish parameters such as fiber protrusion and apex offset are now being required to meet submicron/micron level specifications. Apex offset, which must be less than 50 microns, is presently one of the difficult parameters to achieve with consistency.
It is clear that the use of hand-only polishing methods for fiber optic termini leaves much to be desired in the way of minimizing apex offset. Hand polishing involves the use of pucks, or fixtures, which offer only imprecise control of the terminus. Additionally, differences among human operators result in wide ranging variations between polished termini. As a result, machine polishing is becoming the technique of choice in the fabrication of fiber optic assemblies.
Machines do offer more consistent control, uniformity from one polished terminus to the next, increased productivity, and flexibility between multi-connector and single-connector polishing techniques and fixtures. However, existing machine polishing techniques, to the extent that they contemplate apex offset in the first instance, merely involve the use of machines designed with factory-only apex offset adjustments. Typically, a fiber optic polishing fixture, that is, a puck designed to hold and stabilize a fiber optic ferrule and/or connector in place with respect to a polishing surface during the polishing process, is manufactured taking into consideration machining tolerances to account for a possible apex offset as a function of those tolerances. It is well known that apex offset may be minimized among other things by achieving a high degree of orthogonality of the terminus centerline with respect to the polishing surface. Machining tolerances are taken into consideration with the aim of achieving a desired level of orthogonality.
Factory-only adjustment schemes however are inherently inflexible, as suggested above, mainly because they cannot take into consideration actual variations of terminus orientation with respect to the polishing surface xe2x80x9con-site,xe2x80x9d that is, at the time and place when a user is actually ready to start polishing or is polishing the terminus. Other variations include differences caused by materials such as rubber or resilient pads, abrasive films and lubricants used in the polishing processes. Such variations occur for many reasons, such as, for example, by virtue of the use of upgraded, changed or new connectors on the market, or by virtue of changing the polishing machine or the polishing process, or by virtue of changing the polishing disk. Shimming, or using a shim to prop the terminus into a desired orientation with respect to the polishing surface, is one way to compensate for the above problems. However, shimming does so only very crudely and inefficiently. Although shims for the purpose of allowing apex offset adjustment may be available on the market, they come only in discrete sizes, in this way limiting adjustment possibilities. Theoretically, an infinite range of shim sizes would have to be available to account for every apex offset possibility. Additionally, the shims tend to be compressed in the adjustment process, in this way deforming and leading to unpredictable results in the compensation of apex offset.
Moreover, existing polishing fixtures are typically capable of holding a single type of connector, such that, when new connectors come on the market, new fixtures must be manufactured to accommodate the same. Conventional fixtures involve the actual fixing of the connector to its respective fixture, for example by screwing one into the other, thus limiting the fixture to the screw size used for a specific type of connector. The time and cost for developing new polishing fixtures to accommodate new connectors are usually quite high. Long lead times for such fixtures can have adverse effects on project schedules, not to mention on the cost of the project.
Accordingly, a fiber optic connector polishing fixture is needed that is capable of allowing a simple and effective on-site apex offset adjustment. Additionally, a fiber optic connector polishing fixture that is universal, that is, a polishing fixture configured for supporting fiber optic connectors of varying configurations and diameters would be desirable.
In accordance with the invention, a fiber optic connector polishing fixture assembly for supporting a terminus of a fiber optic cable before a polishing surface is provided. The assembly comprises: a fiber optic polishing fixture adapted to support the terminus before the polishing surface; a fixture support connected to the fixture for supporting the fixture before the polishing surface; and an adjustable connection between the fixture and the fixture support having user accessible adjustment controls for allowing a user to operate the controls to shift the fixture and fixture support relative to one another for substantially eliminating an apex offset of the terminus with respect to the polishing surface.
Preferably, the adjustable connection comprises a set of three adjustment elements including a first adjustment element, a second adjustment element, and a third adjustment element, the adjustment elements being disposed with respect to one another such that, in a cross-sectional plane through the adjustment elements substantially parallel to the fixture support, points corresponding to respective centerlines of the three adjustment elements are not aligned. The first adjustment element is actuatable for effecting a change in the distance between the fixture and the fixture support at a location of the first adjustment element; and the second adjustment element is actuatable for effecting a change in the distance between the fixture and the fixture support at a location of the second adjustment element, an actuation of at least one of the first adjustment element and the second adjustment element effecting a pivoting adjustment of the fixture with respect to the fixture support for substantially eliminating an apex offset of the terminus with respect to the polishing surface.
The assembly herein described allows a user to make precision adjustments to minimize or substantially eliminate measured apex offset in the connector terminus to be polished. In the preferred form, the assembly has a fixture for supporting the terminus and a fixture support for supporting the fixture, and utilizes adjustment screws that allow a user to shift the fixture and the fixture support relative to each other in a precise predetermined manner to substantially eliminate the measured apex offset of the terminus to within the strict specifications mandated for many fiber optic applications. Three adjustment screws may be provided extending between the fixture and fixture support so that turning one of the screws causes pivoting of the fixture about an axis defined by the other two screws. The pivoting of the fixture pivots the connector terminus in relation to the polishing surface so that there is a component of movement of the terminus relative to the polishing surface in two directions perpendicular to one another. Thus, the measured apex offset can be addressed by either turning one screw where the offset from a reference point is only along one of the axes defined by the other two screws, or, as will more likely be the case, by turning both screws where the offset is along both such axes to effect the desired centering of the fiber optic terminus with respect to the polishing surface.
Additionally, the invention provides a method of adjusting apex offset using the assembly described above comprising the steps of: securely fastening the terminus within the terminus support profile of the fixture; moving the three adjustment elements into respective predetermined reference positions; polishing the terminus thereby forming a polished terminus; determining an apex offset of the polished terminus; and actuating at least one of the first adjustment element and the second adjustment element for effecting a pivoting adjustment of the fixture with respect to the fixture support for substantially eliminating an apex offset of the terminus with respect to the polishing surface.
In another form of the present invention, a fiber optic polishing fixture assembly for supporting a terminus of a fiber optic cable before a polishing surface is provided, the assembly including: a fiber optic polishing fixture defining a terminus support profile for supporting the terminus before the polishing surface; a fixture support connected to the fixture for supporting the fixture before the polishing surface; and means for changing a distance between the fixture and the fixture support at at least two point locations for effecting a pivoting adjustment about a third point location of the fixture with respect to the fixture support for substantially eliminating an apex offset of the terminus with respect to the polishing surface.
The invention further provides an assembly as described in the second paragraph of this section, wherein the fixture comprises a jaw movable between an open position and a closed position for securely clamping the terminus therein during a polishing thereof by the polishing surface, and wherein the fixture comprises: a top portion corresponding to a top portion of the jaw; and a bottom portion slidably connected to the top portion. Additionally, the terminus support profile of the fixture includes: a v-groove defined in the bottom portion of the fixture and adapted to receive the terminus therein; a first semicircular recess defined in the top portion; and a second semicircular recess defined in the bottom portion such that, in a closed position of the jaw, the first semicircular recess and the second semicircular recess are joined to define a counterbore framing the v-groove substantially at a center region thereof. The counterbore has a diameter of about 0.50 inch and the v-groove has a depth of about 0.06 inch. The above configuration of the fixture advantageously allows it to be used with connectors having a wide range of diameters.